worktree: parent path should point to the working dir

The working tree's parent path should not point to the parent's gitdir,
but to the parent's working directory. Pointing to the gitdir would not
make any sense, as the parent's working directory is actually equal to
both repository's common directory.

Fix the issue.

src/worktree.c

@@ -174,7 +174,7 @@ int git_worktree_lookup(git_worktree **out, git_repository *repo, const char *na
 	if ((error = git_buf_printf(&path, "%s/worktrees/%s", repo->commondir, name)) < 0)
 		goto out;
 
-	if ((error = (open_worktree_dir(out, git_repository_path(repo), path.ptr, name))) < 0)
+	if ((error = (open_worktree_dir(out, git_repository_workdir(repo), path.ptr, name))) < 0)
 		goto out;
 
 out:
@@ -202,7 +202,7 @@ int git_worktree_open_from_repository(git_worktree **out, git_repository *repo)
 	gitdir = git_repository_path(repo);
 	commondir = git_repository_commondir(repo);
 
-	if ((error = git_path_prettify_dir(&parent, commondir, NULL)) < 0)
+	if ((error = git_path_prettify_dir(&parent, "..", commondir)) < 0)
 		goto out;
 
 	/* The name is defined by the last component in '.git/worktree/%s' */
@@ -457,7 +457,7 @@ int git_worktree_prune(git_worktree *wt, unsigned flags)
 	}
 
 	/* Delete gitdir in parent repository */
-	if ((err = git_buf_printf(&path, "%s/worktrees/%s", wt->parent_path, wt->name)) < 0)
+	if ((err = git_buf_printf(&path, "%s/worktrees/%s", wt->commondir_path, wt->name)) < 0)
 		goto out;
 	if (!git_path_exists(path.ptr))
 	{

src/worktree.h

@@ -24,7 +24,7 @@ struct git_worktree {
 	/* Path to the common directory contained in the parent
 	 * repository */
 	char *commondir_path;
-	/* Path to the parent's .git directory */
+	/* Path to the parent's working directory */
 	char *parent_path;
 
 	int locked:1;

tests/worktree/worktree.c

@@ -118,8 +118,9 @@ void test_worktree_worktree__lookup(void)
 	cl_git_pass(git_buf_joinpath(&gitdir_path, fixture.repo->commondir, "worktrees/testrepo-worktree/"));
 
 	cl_assert_equal_s(wt->gitdir_path, gitdir_path.ptr);
-	cl_assert_equal_s(wt->parent_path, fixture.repo->gitdir);
+	cl_assert_equal_s(wt->parent_path, fixture.repo->workdir);
 	cl_assert_equal_s(wt->gitlink_path, fixture.worktree->gitlink);
+	cl_assert_equal_s(wt->commondir_path, fixture.repo->gitdir);
 	cl_assert_equal_s(wt->commondir_path, fixture.repo->commondir);
 
 	git_buf_free(&gitdir_path);